With increasing demand for data capacities and bandwidth, optical technologies have been successfully developed to facilitate high-capacity transmission of optical data over optical fibre networks. These long-haul networks often use dense wavelength division multiplexing (DWDM) to allow one or more optical sources with different wavelengths to traverse a single optical fibre. Short-haul optical interconnect networks can also use DWDM techniques to increase the data capacity in fibre networks. The networks require stable control of the optical source wavelength in order to keep the optical signal within the passband of one or more optical filters within the DWDM network. A known solution to maintain the wavelength of a DWDM optical source is to design the optical source to emit a single longitudinal mode output, such as a distributed feedback laser (DFB) laser, and then control its wavelength by temperature or electrical current injection in the device. Other complex laser chip designs can be used to achieve wide tunability of the laser wavelength across many wavelengths. However, these methods of wavelength control are one of the major contributions to the electrical power consumption of the optical source and the necessity for cooling restricts the faceplate density of these sources in electrical equipment such as routers and switches. In addition, a DWDM laser device such as a DFB or tuneable laser is complex to fabricate and the yield of fabricated devices at a specified DWDM wavelength is low, leading to a high cost of the laser chip.
The use of injection locking and injection seeding to modify the spectral performance of a Fabry-Perot semiconductor laser has been shown (e.g. Optics Express, Vol. 15, No. 6, p. 2954, 2007) but these demonstrations do not use the incorporation of a phase section in the laser. Alternatively, using distant reflections to wavelength stabilise the laser spectral output have been shown (Optical Fibre Communications 2011, paper OMP4, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 24, NO. 17, p. 1523, Sep. 1, 2012). These multi-wavelength schemes use a shared reflector after a wavelength selective filter but rely on the large distance to de-phase the reflected light with respect to the original laser light.
The use of one or more contacts on a semiconductor laser has been demonstrated, as in IEEE Journal of Selected Topics in Quantum Electronics, Vol. 10, p. 982, 2004, but only to modify the modulation performance of the laser, not to adjust the mode frequencies as in this application.
The use of an external cavity incorporating a filter to modify the spectral response of a laser has been shown in U.S. Pat. No. 6,496,523, but again this does not include the use of a phase section in the laser to tune the mode frequencies with respect to the filter frequency.
Wavelength selectivity improvements in Fabry-Perot semiconductor lasers for wavelength-division multiplexed passive optical networks (WDM-PON) have been demonstrated using external sources to seed either amplified spontaneous emission (H. D. Kim, S. G. Kang, and C. H. Lee, “A low-cost WDM source with an ASE injected Fabry-Perot semiconductor laser,” IEEE Photonics Technol. Lett. Vol. 12, pp. 1067-1069, (2000)) or continuous wave light (“High-speed WDM-PON using CW injection-locked Fabry-Perot laser diodes”, Zhaowen Xu, Yang Jing Wen, Wen-De Zhong, Chang-Joon Chae, Xiao-Fei Cheng, Yixin Wang, Chao Lu, and Jaya Shankar, Optics Express, Vol. 15 No. 6, p. 2953, (2007)). In these examples, there is no monitoring and feedback to control the laser wavelengths.